P0621 — Generator Lamp/L Terminal Circuit

P0621: Generator Lamp/L Terminal Circuit — what it means, the affected system and what to check before replacing parts.

Meaning, symptoms, causes and checks

Generator Lamp/L Terminal Circuit. Basic catalogue definition; diagnostic details have not yet been reviewed.

Affected system: Powertrain

Symptoms

  • Charging warning; fluctuating lighting and discharged battery.

Possible causes

  • Alternator/regulator fault or L-circuit wiring fault.

What to check

  • Check L circuit, connectors and grounds; test charging against specifications.

Also written as: P0621-00, P062100, PO621 (some scan tools add the fault-type byte, e.g. -00).